Improved LTE like initial uplink synchronization via reduced problem dimension

Initial uplink synchronization (IUS) is a random access process in LTE that enables the eNodeB to detect, and uplink synchronize new user equipment. In future networks with huge number of devices, the number of simultaneous IUS users will increase significantly. In addition, it is desirable to serve users moving at high speed. We exploit the structure of the physical random access channel (PRACH) in LTE to reduce the dimension of the underlying data model. This reduction gives a very compact representation of channel impulse response (CIR). We utilize this representation to develop an efficient algorithm which can work in presence of large multiple access interference (MAI) and high carrier frequency offsets (CFO). When compared with the state of the art methods, the proposed method is capable of detecting a significantly higher number of IUS users and can allow high values of CFO. In addition, it produces very reliable estimates of both CIR and CFO of the detected users.